1. Field of the Invention
The present invention pertains to downhole packer tool assemblies, and more particularly, to assemblies comprising the type of packer tool which includes a flexible tubular packer body which is radially extended and retracted with respect to a well bore wall by fluid pressure in a packer set chamber. The features of the invention are particularly advantageous for use in packer assemblies wherein the packer body is of the inflatable type, although the invention may also be used in other types of packers. Likewise, while certain features of the invention are particularly suitable for use in assemblies including two packer tools connected in tandem, at least some of the features of the present invention may likewise be used with assemblies including only a single packer tool.
2. Description of the Prior Art
A modern inflatable packer generally comprises, in addition to the packer body per se, a generally annular upper packer head which is connected to the upper end of the packer body. A tubular mandrel may be connected to the packer head and extends coaxially through the interior of the packer body and out through its lower end. The lower end of the packer body is connected to an annular lower packer head which is slidably disposed in coaxially surrounding relation to the mandrel and sealed with respect thereto.
Thus, an inflation or packer set chamber is defined in the annular space between the mandrel and the interior of the packer body. Some type of inlet is generally provided in the upper packer head in communication with this packer set chamber. The lower end of the mandrel is either closed, or adapted to be selectively closed, as by pumping a suitable plug down through the operating string on which the tool is suspended until it seats on a shoulder provided in the lower end of the mandrel. Then, fluid pressure can be introduced through the operating string to the inlet system in the upper packer head, and thence to the packer set chamber, so as to inflate the packer body.
To accommodate the radial extension of the packer body during such inflation, the lower packer head may slide upwardly on the mandrel. In general, such a tool is likewise provided with some means of setting the packer, i.e. locking it in the inflated condition so that there is no need to maintain pressure in the operating string.
The features described thus far are generally common to all sorts of inflatable packers. More specifically, inflatable packers may, for purposes of the present discussion, be considered as divided into two types. The first type is sometimes called a "multi-set packer." With such a packer, the packer body, once inflated and set, can be released or deflated and subsequently re-inflated and reset downhole, i.e. without being removed from the well for redressing or the like. Prior art multi-set packers have generally been designed so that, when they are released downhole, the fluid in the packer set chamber is emptied into the interior of the packer mandrel and/or the adjoining operating string. This limits the applicability of such mutli-set packers; they are very difficult to use in certain situations, such as those in which the operating string or tubing stands full of liquid, but the annulus between the operating string and the well bore wall is not full. The difficulty of emptying the fluid within the packer set chamber into the interior of the operating string or tubing under such circumstances can readily be appreciated.
The other major general type of inflatable packer is commonly known as a "single set packer." In general, prior art single set packers have been usable in the aforementioned situations which are not well suited for conventional multi-set packers. This is because a single set packer typically may be released downhole by emptying the contents of the packer set chamber into the annulus between the operating string and the well bore wall. Thus, the tool can easily be released even if the operating string stands full of liquid. However, typical prior art single set packers suffer from the disadvantage, implied by their name, that they cannot be reinflated and reset downhole. Thus, once a single set packer has been released, a trip to the surface is necessary before the well bore can be once again packed off.